Laser-ion acceleration via anomalous electron heating

TL;DR

This study demonstrates that high-contrast picosecond laser pulses can efficiently accelerate ions via anomalous electron heating, achieving high proton energies and energy conversion efficiencies relevant for fast ignition and ion beam applications.

Contribution

It introduces a new understanding of anomalous electron heating in laser-ion acceleration and develops a plasma expansion model incorporating this effect.

Findings

Achieved 52 MeV proton energies at 1.2×10^19 Wcm^-2

Demonstrated 5% energy conversion efficiency with 6 ps pulses

Validated the model with experiments and simulations

Abstract

Using a kilojoule class laser, we demonstrate for the first time that high-contrast picosecond pulses are advantageous for ion acceleration. We show that a laser pulse with optimum duration and a large focal spot accelerates electrons beyond the ponderomotive energy. This anomalous electron heating enables efficient ion acceleration reaching 52 MeV at an intensity of 1.2X10^19 Wcm^-2. The proton energy observed agrees quantitatively with a one-dimensional plasma expansion model newly developed by taking the anomalous heating effect into account. The heating process is confirmed by both measurements with an electron spectrometer and a one-dimensional particle-in-cell simulation. By extending the pulse duration to 6 ps, 5% energy conversion efficiency to protons (50 J out of 1 kJ laser energy) is achieved with an intensity of 10^18-Wcm^-2. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines.